how to facet
gemstone main cabochon creation
mineral data
Mineral Name: zoisite
Gem Names: tanzanite - thulite - ruby zoisite
Chemistry: Ca2Al2(AlOH)(SiO4)3
Class: silicate - sorosilicate
Crystal Sys: orthorhombic
Hardness: 6.0 - 6.5 Specific Gravity: 3.25 - 3.37
Fracture: uneven to conchodial Refractive Index: 1.70 - 1.706
Dispersion: 0.030 (high)
Misc Prop: Zoisite is the general mineral name and there are three varieties used for jewelry and all are very different. Thulite is a pink colored, opaque to slightly translucent material usually found in large masses and not crystalline.

Thulite is normally cut in to cabochons for jewelry use, but has not seen wide spread use. Some of the best material comes from Norway. It has a varied texture and is rarely color consistent It often has a mottled look. Its color originates from manganese.

"ruby in zoisite" is another material and often used in carvings. The zoisite in this case is green and is the background material for the red opaque ruby crystals. The green color comes form the zoisite containing chromium. (Chromium being the coloring agent in the ruby.)

The king of the gemstone zoisites is "tanzanite", a relatively new comer on the scene that has been found at only one locality in Africa. The best tanzanite is dark blue to violet-blue and is often heat treated material. The undesirable yellow to yellow-brown coloration can be destroyed by heating and the blue color usually intensifies.

Tanzanite has grown in popularity and can now be found in most jewelry stores, it is no longer a "collectors" stone. The market has a good deal of less valuable, very pale blue, transparent material currently available. There are constant rumors about loss of availability as the locale is not in the most stable part of the world.

Color: In gemstones, color, is often the key to naming or describing the particular variety. Hence look for this information below in the various descriptions. Color, opacity, and homogeneity often determine the placement of value on any given stone, and are all optical properties of the particular stone.
Specific Data:
2 pink cabs
a rectangular cut stone